A liquid action substance battery employing an alkaline metal such as lithium, sodium or potassium, or its alloy as the negative pole action substance and oxyhalide such as thionyl chloride, sulfuryl chloride or phosphoryl chloride in a liquid state at normal temperature as the positive pole action substance, is commonly used, for example as a backup power source for a memory used in various industrial equipments, for its characteristics of large energy density, of excellent storage capacity and of availability over wide range of temperature.
In this battery, the negative pole action substance consisting of alkaline metals or its alloys is generally press-bonded to the inner surface of the can doubled as a negative pole terminal, and the positive pole substance mainly consisting of porous carbon is mounted in the can with a separator their-between. The liquid action substance mainly consisting of said oxyhalid, which is a positive pole action substance doubled as an electrolyte, is stored in the can. In addition, said positive pole substance is consisted of porous carbon and positive pole current collector such as metallic mesh or metallic rod.
In the liquid action substance battery as mentioned above, the negative pole action substance directly contacts with the positive pole action substance. However, since a protective coating which is chemical reaction products (alkaline metal halide salt such as lithium chloride) between the negative pole action substance and the positive pole action substance or electrolyte melted in the substance, is formed on the surface of the negative pole action substance, accordingly said coating could prevent direct reaction between the negative pole action substance and the liquid positive pole action substance doubled as electrolyte, and could prevent from self-discharging of the battery as well, and therefore it contributes to keep the battery safe, for example by preventing from heat generating.
In other side, these batteries are usually connected to the external terminals or connectors for their use, accordingly the external terminals or leading foils are commonly welded to the bottom face or top face of the battery, for example by spot welding.
However, in case that welding heat is directly transmitted to the negative pole action substance while welding of the external terminal to the bottom face of the battery can, the negative pole action substance might be melted. Accordingly it can't keep separate the negative pole action substance against the positive pole action substance by mean of the protective coating covered over the surface of said negative pole action substance. Then the negative pole action substance immediately reacts with the positive pole action substance in the cell, thereby inner pressure in the cell being increased, accordingly the explosion-proof valve consisting of cross-like thin plates placed on the bottom of the can happen to be torn apart.
In order to avoid such risk as mentioned above occurred in welding the external terminal to the bottom surface of the can, the position of the welding of the external terminal on the bottom surface of the can has been commonly shifted to the near center of the bottom surface, not to the peripheral part of the bottom surface of the can where the negative pole action substance is located nearby.
However, in case that press-bonding position of the negative pole action substance to the can would be off the point and the negative pole action substance would extrude to the bottom face of the can, the welding heat would be transmitted to the negative pole action substance while welding of external terminal, accordingly internal pressure in the can is increasing and as a result the explosion-proof valve rarely happen to be torn apart.
JP6-68863A showed a measure to deal with such a problem as mentioned above. The measure described in the documents primarily deal with the disruption of explosion-proof valve before it works, in case that the liquid action substance battery happens to fall down in the soldering pot, immediately thereby the battery would be exposed to large amounts of heat with high temperature. However, as a secondly effect, the measure could be against the danger of the disruption of the can while welding of the external terminal, by means of inserting a resin ring such as poly-tetra-fluoro-ethylene, etc. in the bottom of the battery can.
However this measure has some disadvantages as mentioned below. In view of thermal stability and resistance against oxyhalide, fluororesin such as poly-tetra-fluoro-ethylene, etc. are used as a resin ring. But the fluororesin is not preferable because lithium fluoride is formed in the reaction of the fluororesin with lithium used as the negative pole action substance. Moreover, in view of structural and manufactural restriction, the resin ring should be inserted beforehand in the bottom of the battery can before the negative pole action substance is press-bonded to the inner surface of the can. In that case, however, vibration and static electricity generated during transferring process of resin ring after insertion in the battery can, happen to make the resin ring disorder or slant. Therefore said measure is not preferable in view of mass production of the batteries.
The purpose of the invention being made in view of aforementioned circumstances, is to enhance the safety of the liquid action substance battery having its external terminal welded after assembling the battery so as not to be tore apart in the subsequent welding work of the external terminal, even if the position of the negative pole action substance being press-bonded to the inner surface of the battery can would be shifted and that substance would be extruded to the bottom face of the battery can.